Additives have been used by many companies to try to improve engine performance. An additive or additive package may be used for a variety of purposes, such as detergency, reducing engine wear, stability against heat and oxidation, reducing oil consumption, corrosion inhibition, to act as a dispersant, and to reduce friction loss. Reducing friction loss is of great interest because of its impact on fuel economy performance. As such, friction modifiers have been given much attention.
It has been proposed in many patents and articles (for example, U.S. Pat. Nos. 4,164,473; 4,176,073; 4,176,074; 4,192,757; 4,248,720; 4,201,683; 4,289,635; and 4,479,883) that oil soluble molybdenum is useful as a lubricant additive. In particular, molybdenum provides enhanced fuel economy in gasoline or diesel fueled engines, including both short and long term fuel economy (i.e., fuel economy retention properties). The prior proposals typically use molybdenum at levels greater than 350 ppm up to 2,000 ppm in additive packages, which contain one or more detergents, anti-wear agents, dispersants, friction modifiers, and the like.
Durability of engine lubricants is becoming an important issue. Today's lubricating oils quickly lose their ability to provide beneficial enhancements to engine performance. This makes it necessary to frequently change the engine's oil. As such oil consumption and maintenance costs increase, leaving car owners with an undesirable burden.
To address this problem, the present inventors have developed a lubricating oil composition that provides initial engine performance benefits and retention of those benefits for a longer period of time than with oils currently available in the marketplace. The composition is less volatile, which enables a greater percentage of the lubricating oil composition to remain in the engine over time. This leads to an improvement in fuel economy and fuel economy retention. Moreover, less maintenance is required, since drainage intervals are extended.
The present inventors have also found that low temperature valve train wear performance, fuel economy and fuel economy retention properties, can be improved to meet the requirements of the next generation of motor oil certification such as the proposed ILSAC GF-3 standards (International Lubricants Standardization and Approval Committee), using much lower levels of molybdenum than currently required in conventional additive packages.